Variable inductive coupler



March 11, 1952 K. MUNSON 2,583,406

VARIABLE INDUCTIVE COUPLER Filed Oct. 25, 1948 2 SHEETSSHEET 1 ILL-21L INVENTOR. IVAN KE\TH MUNSON BY W ATTORNEY.

March 11, 1952 1.1K. MUNSON 8,

VARIABLE INDUCTIVE COUPLER Filed Oct. 25, 1948 2 SHEETS-SHEET 2 fuzz- .1; 1152.5

JNVENTOR. IVAN KEITH MUNSON BY W 4 ATTORNEY.

Patented Mar. 11, 1952 UNITED STATES PATENT OFFICE 9 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates to variable radio-frequency inductive couplers and is particularly usefill in electronic circuits for coupling the balanced outputs of two tubes to the input of a single succeeding tube.

The prior art contains many devices for varying the magnetic coupling between two or more coils by varying their physical relationship in space. While these devices are generally satisfactory in operation, they involve the use of relatively complex and bulky mechanical structures. It is of the utmost importance that the component parts of a circuit handling high radio frequency currents be arranged in close physical proximity and in an electrically balanced configuration. The

intimate physical relationship of the components in such a circuit precludes the use of conventional variably coupling devices. and puts a premium on extremely simple and compact designs. It is therefore the general object of this invention to provide a simple and compact variable radiofrequency inductive coupler having no metallic operating parts. It is another object to provide a variable coupling transformer having two primary coils which may be simultaneously moved to and from a stationary secondary coil, the coupling between one primary coil and the secondary coil being always equal to the coupling between the other primary and the secondary coil.

It is a further object to provide a variable coupling transformer having coils and a single member for varyingthe spacing of the coils. 7

It is a further object to provide a novel variable inductor of extremely simple construction.

In pursuance of these and other objects which will be apparent to those skilled in the art,.-. a cylindrical rod of insulating material is provided having a circular groove on the central portion of the rod, a right-hand helical groove on one side of the central portion and a left-hand helical groove on the other side of the central portion. A secondary coil is wound in the circular groove and helical primary coils are positioned in the helical grooves. The helical coils of wire in each of the helical grooves are prevented from rotation by support means so that the helical coils may be moved axially to and from the centralsecondary coil by rotating the rod.

For a better understanding of the invention, reference is had to the following description taken with the accompanying drawings wherein:

' Figure 1 is a top plan of one physical embodiment of the invention.

' Figure 2 is a front elevation of the same.

Figure 3 is a schematic diagram of the invention connected for use as a variable transformer having two inputs and one output.

Figure 4. is a schematic diagram of the inven-' tion connected for use as a variable transformer having one input and one output.

Figure 5 is a schematic diagram of the invention connected for use as a variable inductor.

Figure 6 is a physical embodiment of the same, part of the rod being broken away to show a slug of poly-iron imbedded therein.

Referring now in greater detail to Figures 1 and 2 of the drawings, the variable transformer has a base plate Ill provided with mounting screw holes H, l l on the end portions thereof. Upright side members l2 and is mounted on the base plate ii] are provided with coaxial bearing apertures i4 and I5 respectively. Guide bars I6 and I! extend between the side members l2 and.l3,' and are provided with longitudinal slots 18 and I9 respectively. The base and side members thus far described are preferably made of an insulating plastic material.

A cylindrical rod generally designated 20 is constructed of an insulating plastic material, such as polystyrene, characterized by having a very low dielectric loss when subjected to high frequency radio energy. The cylindrical rod 20 has end portions 2| and 22 of reduced diameter which are journaled in the bearings I 4 and I5 of the side members I2 and I3. The end portion 22 extending from the side member I3 is provided with a cerf 23 to permit rotation of the cylindrical rod 20 by means of a screw driver. The other end 2| of the cylindrical rod 26 is provided with a crank arm 24 for manual rotation of the cylindrical rod 26. The cerf 23 and the crank arm 24vv are alternative constructions, one or the other may be provided according to the mode of operation desired. Y

The central portion of the rod 2Eiis provided with an annular groove designated 25 formed between two circular beads 21 and 28. A right helical groove 38 is provided on the surface of the cylindrical rod 20 on one side of the central annular groove 26, and a left hand helical groove 3! is provided on the other side of the central annular groove 26. l

.A helical coil 32 is'wound to conform with the pitch and diameter of the helical groove 30. The ends 33 and 3 of the coil 32 extend through the longitudinal slot IS in the guide bar II. Another helical coil 35 is wound with the samepitch and diameter as the helical groove 3|. The ends 35 and 37 of coil 35a1so extend through the ion- 3 gitudinal slot IQ of the guide member IT. The helical coils 32 and 35 are designed to fit snugly in the helical grooves 30 and 3| respectively and yet be loose enough to permit rotation of the cylindrical rod 20 without causing rotation of the helical coils 32 and 35. The helical coils 32 and 35 will ordinarily be employed as primary coils and will be herein so designed, but of course, the connection may be reversed so that they are employed as secondary coils.

A secondary coil 38 is provided in the central annular groove 26, the coil having leads 39 and 40 extending through the longitudinal slot is in the guide member [6. The secondary coil 38 is located equi-distant from the helical coils 32 and 35, is prevented from axial movement by the beads 21 and 28, and is prevented from rotation by the guide member IS. The secondary coil 38 fits loosely enough in the groove 26 to permit rotation of the cylindrical rod 23 without causing rotation of the secondary coil 38. It is apparent that the secondary coil 38 is at all times maintained in a stationaryposition in coaxial relationship with the helical coils 32 and 35.

In the operation of the transformer, the coupling between the helical primary coils 32 and 35 and the secondary coil 38 may be varied by rotating the cylindrical rod 20 with a screw driver or by manually turning the end crank 24. Since one of the helical grooves 30 and 3| is a right hand helix and the other is a left hand helix, turning of the cylindrical rod in one direction will cause the helical coils 32 and 35 to move toward the secondary coil 38, always maintaining an equal spaced relationship therebetween. When the cylindrical rod 20 is rotated in the opposite direction the helical coils 32 and 35 are made to move axially away from each other and away from the secondary coil 38, always maintaining a balanced spaced relationship. The axial movements of the helical coils 32 and 35 results from the action of the guide bar in preventing rotation or the helical coil. The construction employed is such that the friction between the coils and the rod 20 will maintain the coils in any spaced relationship to which they are moved. No stop or holding mechanism of any kind is required.

It is within the contemplation of this invention that the cylindrical rod 20, and the coils 32, 35 and 40 may be employed in a circuit without the base plate ID, the end bearing members I2 and I3 or the guide members l6 and I1. When so employed, the coil leads 33, 34, 36, 31, 39 and 40 will beof sufi'lcient thickness to render the struce ture self supporting. The various leads will then be connected directly to the adjacent circuit elements and the cylindrical member 23 will be supported in mid air by the coil. This arrangement permits the use of very short leads and the intimate physical relationship of the various circuit elements. The various leads being. directly connected to the other circuit elements which are anchored to the chassis of the equipment, the

coils are prevented from rotation when the cylindrical rod 26 is rotated to vary the coupling between the coils. The cylindrical rod 20, of course, maintains the coils at the proper coaxial physical relationship.

. Figures 3. and 4 illustrate two difierent ways of connecting the coils 32, 35 and 38. In Figure 3, the output of two balanced circuits may be connected at 43 and 42 respectively to the primary coils 32 and 35. The energy induced in the secondary coil 38 is always equally the result of the inputs at 42 and 43, regardless of the positions of the coils 32 and 35. In Figure 4, a single input is applied to the primary coils at 44, there being a jumper 45 of flexible material connecting one side of each of the coils 32 and 35. Various other methods of utilizing the variable coupling transformer of this invention will be apparent to those skilled in the art.

Figs. 5 and 6 illustrate the use of the invention to provide a variable inductor, the inductance between the points 46 and 41 being variable by adjusting the relative position of the two coils 32 and 35. A jumper 48 of resilient material is connected between the ends of both coils. A slug of poly-iron 49 is centrally and coaxially disposed in the interior of the cylindrical rod 20. The slug of poly-iron in the center of insulating rod 20 is operative to lower the magnetic reluctance of the field and effectively increase the range over which the inductance between points 45 and 41 may be varied as the spacing of coils 32 and 35 is varied by rotating the rod 20.

It is apparent that a very simple and effectve device has been provided for varying the coupling between a plurality of coils, the coils being at all times maintained in a balanced physical and electrical relationship.

While the invention has been shown and described in connection with specific embodiments, it will of course be understood that the invention is not limited thereto, since it is apparent that the principles herein disclosed are susceptible to numerous other applications, and modifications may be made without departing from the spirit and scope over the invention as set forth in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes, without the payment of any royalties thereon or therefor. I

What is claimed is: p I p 1. A variable coupling transformer comprising a cylindrical rod of insulating material journaled for rotation, the rod having a helical groove of uniform pitch and diameter on one portion thereof and an annular groove on another portion, a helical coil of wire slidably wound in the helical groove, and a second coil of wire slidably wound in the annular groove, means for rotating the rod'and support means for preventing the rotation. of the coils whereby, upon rotation of said rod, the helical coil of wire is axially moved along'the rod and the second coil remains in a fixed position with respect to the longitudial axis of said rod. 7 v

I 2. A variable coupling transformer comprising" a rod of insulating material journaled for rotation, the rod having a centrally located annular groove, and a helical groove on each side of the circular groove, a helical coil of wire wound in each of the helical grooves, a third coil of wire disposed in the annular groove, means for rotating the rod and support means for preventing rotation of the coils.

3. A variable coupling transformer comprising a rod of insulating material journaled for rotation, the rodhaving a right-hand helical groove on one side of its central portionand a left-hand helical groove on theother side of the central portion, a helical coil of wire wound in each of the. helical grooves, a third coil of wire positioned a rod of insulating material having a right-hand helical groove on one side of its central portion and a left-hand helical groove on the other side, a helical coil of wire wound in each of the helical grooves, and a third coil of wire on the central portion of the red, the ends of the coils being adapted for connection directly to other circuit elements thereby preventing rotation of the coils about their common axis, and engageable means on the rod for rotation thereof.

5. A variable coupling transformer comprising a rod of insulating material having a centrally located annular groove, 2. right-hand helical groove on one side of the central groove, and a left-hand helical groove on the other side of the central groove, a secondary coil wound around the rod in the central annular groove, a helical coil of wire wound in each of the helical grooves, the ends of the coils being adapted for connection directly to other circuit elements thereby preventing rotation of the coils about their common axis, and engageable means on the rod for rotation thereof.

6. A variable inductor comprising a base, a rod of insulating material journaled on the base, the rod having a right-hand helical groove on one side of the central portion and a left-hand helical groove on the other side, a helical coil of wire wound in each of the helical grooves, and a flexible jumper connecting one end of each coil, the other ends of the coils being terminals of the inductor, whereby rotation of the rod is operative to change the inductance between the terminals.

7. The inductor defined in claim 6 wherein a slug of magnetic material is positioned coaxially within the central portion of the rod.

8. A variable inductance device comprising a rod of insulating material journaled for rotation, a right hand helical groove formed in one side of said rod and a left hand helical groove formed in the other side of said rod, a helical coil of wire wound in each of said grooves, means for rotating the rod and support means for preventing rotation of the coils.

9. The device of claim 8 wherein the pitch of said grooves are substantially equal in opposite senses.

IVAN KEITH MUNSON REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,701,330 Medved Feb. 5, 1929 2,138,330 Thompson Nov. 29, 1938 2,452,679 Ramsden Nov. 2, 1948 2,458,071 Gordon Jan. 4, 1949 FOREIGN PATENTS Number Country Date 439,147 Great Britain Nov. 29, 1935 467,862 Great Britain June 24, 1937 445,034 France Oct. 31, 1912 

